Overcoming the rate-distance limit of quantum key distribution without quantum repeaters
Overcoming the rate-distance limit of quantum key distribution without quantum repeaters
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DOI：
10.1038/s41586-018-0066-6
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发表时间：
2018-05-17
期刊：
影响因子：
64.8
通讯作者：
Shields, A. J.
中科院分区：
文献类型：
--
作者：
Lucamarini, M.;Yuan, Z. L.;Shields, A. J.
量子密钥分发（QKD）（1，2）允许两个远程方共享加密密钥，并基于物理定律进行安全性。在实验上，QKD已经通过光学手段实现，在50公里的标准光纤上实现了每秒1.26兆比特的密钥速率（3），在404公里的超低损耗光纤上实现了每小时1.16比特的密钥速率（4）。提高QKD的比特率和范围是一个艰巨但重要的挑战。目前被认为在没有量子中继器的情况下不可行的相关目标（5-7）正在克服QKD的基本速率距离限制（8）。该限制定义了双方可以使用QKD在给定距离处传输的最大可能的密钥速率，并且通过连接双方的量子信道（9）的密钥容量来量化。在这里，我们介绍了一种替代方案的量子密钥分配，即相位随机光场对首先产生在两个遥远的位置，然后在一个中央测量站组合。具有相同随机相位的场是“孪生”，可以用来加密量子密钥。这种双场QKD的密钥速率表现出与量子中继器相同的距离依赖性，与信道透射率的平方根成比例，而不管谁（恶意或其他）控制测量站。然而，与涉及量子中继器的方案不同，我们的方案在当前技术下是可行的，即使在550公里的标准光纤上也能提供可管理的噪声水平。该方案是克服量子密钥分发速率-距离限制和大大扩展安全量子通信范围的一个有希望的步骤。
Quantum key distribution (QKD)(1,2) allows two distant parties to share encryption keys with security based on physical laws. Experimentally, QKD has been implemented via optical means, achieving key rates of 1.26 megabits per second over 50 kilometres of standard optical fibre(3) and of 1.16 bits per hour over 404 kilometres of ultralow-loss fibre in a measurement-device-independent configuration(4). Increasing the bit rate and range of QKD is a formidable, but important, challenge. A related target, which is currently considered to be unfeasible without quantum repeaters(5-7), is overcoming the fundamental rate-distance limit of QKD(8). This limit defines the maximum possible secret key rate that two parties can distil at a given distance using QKD and is quantified by the secret-key capacity of the quantum channel(9) that connects the parties. Here we introduce an alternative scheme for QKD whereby pairs of phase-randomized optical fields are first generated at two distant locations and then combined at a central measuring station. Fields imparted with the same random phase are 'twins' and can be used to distil a quantum key. The key rate of this twin-field QKD exhibits the same dependence on distance as does a quantum repeater, scaling with the square-root of the channel transmittance, irrespective of who (malicious or otherwise) is in control of the measuring station. However, unlike schemes that involve quantum repeaters, ours is feasible with current technology and presents manageable levels of noise even on 550 kilometres of standard optical fibre. This scheme is a promising step towards overcoming the rate-distance limit of QKD and greatly extending the range of secure quantum communications.